Field of the Invention
The present invention relates to an oil-in-water type emulsified cosmetic. More specifically, the invention relates to an oil-in-water type emulsified cosmetic which has the effect of beautifying the appearance of skin, while also excelling in emulsion stability.
Description of the Related Art
Titanium oxide is widely used in cosmetics, naturally as white pigments, and due to having a high refractive index, as covering agents for adjusting skin tone such as dullness or redness of the face, concealing color irregularities such as spots and freckles, and improving the appearance of the skin beautifully, and as UV protectants by physically scattering and absorbing UV rays at the particle surface.
When used as covering agents, titanium oxide or titanium oxide agglomerate particles having an average particle size of at least 0.1 μm are generally used. For example, in Patent Document 1, a cosmetic that combines titanium dioxide having an average particle size of 0.1 to 0.5 μm and titanium dioxide of 0.5 to 1.5 μm is described as having a natural skin color and excellent covering ability. Additionally, in Patent Document 2, a cosmetic containing rutile-type titanium dioxide agglomerate particles having a particle size of 0.1 to 5.0 μm is described as excelling in spreadability and sense of finish, excelling in skin coloring ability and concealing ability, and presenting a sense of bare skin without over-coloration.
On the other hand, when used as a UV protectant, fine-particle titanium oxide with an average particle size of less than 0.1 μm, typically 0.05 μm or less, are generally used. For example, Patent Document 3 describes that a cosmetic with abundant UV protection ability, high transparency and no paleness can be obtained by using an ultrafine-particle titanium oxide with an average particle size of 0.005 to 0.05 μm which has been subjected to a specific surface treatment.
In order to blend such particulate powders into a product and achieve lasting effects, the powder must be adequately dispersed in the cosmetic, but powders of small particle size are strongly cohesive, and tend to have inferior dispersibility and emulsion stability. Therefore, in the case of a liquid product, dispersion by mechanical force is not enough, and the emulsion stability must also be improved so that agglomeration does not occur over time.
As a cosmetic with improved stability and dispersibility of fine-particle powders, for example, Patent Document 4 proposes a sunscreen oil-in-water type emulsified cosmetic wherein a powder functioning as a UV scattering agent is subjected to a specific surface treatment, and dispersed using specific oils and dispersion agents.
Additionally, Patent Document 5 indicates that by blending a sunscreen agent, a structuring agent, a hydrophilic surfactant, a thickening agent and water, a gel network structure, liquid crystal structure or both can be formed in the composition, thereby suppressing the destruction of active components and destabilization due to the water in the composition.
However, Patent Documents 4 and 5 both relate to sunscreen cosmetics, and therefore have the purpose of improving the dispersibility of mainly fine-particle powders used as UV scattering agents, i.e. powders generally having an average particle size of less than 0.1 μm, so they are not intended to improve the stability and dispersibility of powders of larger average particle sizes. In general, as the particle size of a powder becomes larger, the cohesive force becomes smaller, and dispersion becomes easier because less dispersion energy is consumed, so there is thought to be a tendency towards improved emulsion stability. However, upon applying these findings described in Patent Documents 4 and 5 to hydrophobized titanium oxide having a skin improvement effect and with larger average particle sizes, the present inventors observed that sufficient emulsion stability was not obtained.
Additionally, while titanium oxide has a higher surface activity than zinc oxides and are considered to be more difficult to disperse than zinc oxides, Patent Document 4 specifically uses zinc oxides as UV scattering agents, and Patent Document 5 does not provide any concrete examples containing titanium oxide as sunscreen agents.
Therefore, an oil-in-water type emulsified cosmetic that stably disperses a hydrophobized titanium oxide having an average particle size of at least 0.1 μm, and that is capable of beautifully improving the appearance of the skin, is sought.